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From: Edmond Lau <edmond@ooyala.com>
Date: Fri, 13 Nov 2009 00:31:52 -0800
Message-ID: <f05b8c590911130031q751f93d4ga821b07bb96e77bb@mail.gmail.com>
Subject: Re: newbie questions about Cassandra J. Ellis presentation
To: cassandra-user@incubator.apache.org
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On Fri, Nov 13, 2009 at 12:20 AM, TuxRacer69 <tuxracer69@gmail.com> wrote:
> Hello Cassandra Users!
>
> On the wiki page:
> http://wiki.apache.org/cassandra/ArticlesAndPresentations
> there is a link to J. Ellis pdf:
> http://assets.en.oreilly.com/1/event/27/Cassandra_%20Open%20Source%20Bigtable%20+%20Dynamo%20Presentation.pdf
>
>
> At page 41 we have: (Roadmap) Cassandra 0.5
> Cassandra 0.5
> Millions of columns per row
> This will require another data format change
>
> Question 1:
> -----------------
> Is there any Jira logged for this change yet?
> I'd like to understand
> a) if a full data rebuild will be necessary for upgrading from 0.4.X to 0.5
> b) what the limitations currently are in Cassandra.
> - How many keys per column family
> - How many columns per key in a standard column family
> - How many columns per key in a super column family, and how many subcolumns
> within a supercolumn key
>
> Page http://wiki.apache.org/cassandra/CassandraLimitations
> says "The main limitation on column and supercolumn size is that all data
> for a single key and column must fit (on disk) on a single machine in the
> cluster." but that does not really answer the questions above (as know we
> can have 1Tb disk cheaply)
>
> Question 2:
> ----------------
> Page 15 and 16: Architecture layer.
> How could we defined Memtables and SStables? What the two 'S' stand for in
> SSTable?

A Memtable is Cassandra's in-memory representation of key/value pairs
before the data gets flushed to disk as an SSTable.  An SSTable
(terminology borrowed from Google) stands for Sorted Strings Table and
is a file of key/value string pairs, sorted by keys.

Edmond

>
> Thanks a lot
> Alex
>
>
>